Recently, the scientists of the Event Horizon Telescope project announced that they had taken a picture of a black hole in the M87 galaxy 50 million light-years from earth. It is an extraordinary scientific and engineering achievement. Is this definite proof that black holes exist?
The astrophysics community certainly thinks so. Director of the Max Planck Institute for Radio Astronomy Michael Kramer declared that “the history of science will be divided into the time before the image, and the time after the image.”
A light-year is the distance that light travels in one year. The moon is only 1.5 light-seconds away. Taking a picture of the M87 black hole is the equivalent of photographing a pebble on the moon from Earth. It was achieved by using multiple radio telescope systems across the world, making a telescope lens the size of the earth.
The downside is that each telescope in the project captured only a piece of a gigantic jigsaw puzzle. An equally important part of the effort was to develop algorithms to stitch the pieces together into a photo.
To those who are not up to speed on modern physics: In the early 20th century, Albert Einstein posited a new theory of gravity based on matter warping space and time, which is best thought of as a lensing effect. Just like a lens bends rays of light passing through it, so does gravity near a massive body, like the sun. The result is that clocks near matter tick slower than those far away from it, and we experience the lensing in the form of gravity. The force we feel pulling us to the ground is space and time “bending” us downward.
Sounds crazy, but it is a surprisingly well-tested theory. The GPS satellites that allow us to pinpoint the location of things on Earth wouldn’t work without clock adjustments, because the satellites up there feel less gravity than we do down here, and therefore their clocks run slightly faster than ours.
But what if an enormous amount of matter was densely packed into such a small region that the fabric of spacetime went haywire? That is essentially what a black hole is. Such a body bends light so much that, at a certain distance from its center, light can no longer escape. That is what is known as the event horizon of the black hole.
The picture released by the Event Horizon Telescope project depicts an object that precisely fits the predicted description of such an object.
However, at the center of a black hole, according to Einstein’s theory of general relativity, something strange happens: Spacetime breaks completely down into a singularity. That’s a fancy way of saying that the formulas end up with a division by zero, which most kids in school have learned is a big no-no.
Usually, if a theory produces a singularity, it is a sure tell that there is something wrong. Nevertheless, in this case, physicists take it seriously because general relativity works so well in all other areas.
The Greatest Sin
There is no greater sin in science than to extrapolate a theory beyond observational data. In this case, the scientists have unquestionably taken a picture of a real object that fits the predictions of what a black hole should look like, but the infinitely dense point-shaped singularity at the center remains speculation.
It could be true, but the history of science has not been kind to singularities or extrapolations far beyond observation. Virtually every successful theory of science has run into trouble when pushed to the edge, requiring each one to be modified. Is the singularity at the center of the black hole where Einstein’s model of gravity finally breaks down? We don’t know, but history says yes.