Doug Bonderud

Apr 26th 2021

First Image of Black Hole Shadows Suggests Einstein Was Right — Again


Don’t bet against Albert Einstein. The popular physicist famously asserted that “God does not play dice with the universe,” and recent observations seem to confirm the regularity, not randomness, of the phenomena examined in Einstein’s theory of general relativity. Of course, this hasn’t stopped scientists and laypeople from trying to find pitfalls or loopholes in his theory, but as the first image of black hole shadows suggests, Einstein was right — again.

So let’s look at how this supermassive snap supports the theory of general relativity, why it helps rule out alternative explanations, and what it doesn’t say about life, the universe and everything.

Shadow and Light

In April 2019, the first-ever image of a black hole was published. While the snap of galaxy M87’s supermassive monster may not look like much (it’s effectively a fuzzy, slightly lopsided yellow donut surrounding a dark center), it once again supports Einstein’s theory. Here’s why: Not only did the theory of general relativity predict the existence of black holes; it also predicted the size of a shadow cast by a black hole on its surrounding disc of material.

The new image offered a way to test Einstein’s theory again and discover whether its constructs would break down and diverge from observed reality under extreme conditions. Spoiler alert: They did not. As Science News noted, “the shadow closely matched general relativity’s predictions of size.” The work of another famous physicist, Stephen Hawking, helped to improve our understanding of interactions between matter and gravity around black holes and also helped to explain why we can “see” these insatiable space-eaters with the right equipment.

When matter gets close to a black hole’s event horizon, some of it forms an orbiting disc that heats up as particles bump into each other. More matter means more friction and more heat, which in turn generate light. Using the Event Horizon Telescope (EHT), scientists were able to detect and measure the light from this matter mashup and “see” the corresponding darkness of the black hole itself. This allowed teams to perform “second order” calculations, such as shadow size measurements that aren’t possible closer to home, and lend further credence to Einstein’s theory.

It’s All Relative

This isn’t the first time Einstein’s theory of general relativity has been challenged through observation. The first opposition came more than a century ago, when Einstein’s assertion about the “warping” of spacetime due to gravity put him at odds with another of history’s towering scientific figures, Sir Isaac Newton. In Newtonian frameworks, light had no mass and therefore could not have its speed or direction altered by gravity. Einstein saw things differently and suggested that sufficiently massive objects, such as planets, stars or black holes, could curve the fabric of spacetime, effectively forcing light to change course.

A solar eclipse offered an opportunity to test Einstein’s theory. If he was right, the apparent positions of stars would seemingly shift when their light passed through our sun’s gravitational field. Since staring into the sun on an average day is both a bad idea and unlikely to return any useful data, astronomer Arthur Eddington and his team packed up their telescopes and headed to a small island off the coast of Africa. During an eclipse they took measurements of stars near the sun and — lo and behold — Einstein was right.

His theory got another boost in 2016 when scientists at the Laser Interferometer Gravitational-Wave Observatory (LIGO) confirmed the existence of gravitational waves, which formed a key component of Einstein’s theory but had never been verified through observation. Not only did the LIGO team detect the waves, but it also traced them to a black hole collision that happened more than 1.3 billion years ago — not bad for a theory that’s just over 100 years old.

Give Me a Break

Despite repeated confirmation of Einstein’s theory, scientists are still looking for ways to “break” relativity and uncover new spatial interactions. It’s just good science; theories require ongoing analysis to ensure that their predictions match reality, and more answers about the nature of gravity, mass and light could form the foundation for grand unified theories that have so far eluded scientific scrutiny.

The good and bad news is that Einstein’s theory still holds up. From curving spacetime to gravitational waves to black hole shadows, general relativity continues to deliver in scientific show-downs. This makes it an incredibly useful tool for assessing the state of the universe, but it can also be frustrating for researchers looking for a new take on universal forces. However, as Lia Medeiros of the Institute for Advanced Study in Princeton, New Jersey, notes, while new research might make it harder to find cracks in relativity, “we haven’t made it infinitesimal.”

Think of it like a box: While a bigger box may offer more space to go looking for new theories about spacetime, it also means more space for potential dead-ends. By confirming that Einstein was generally correct about general relativity, researchers have shrunk the box and perhaps reduced the number of possible paths to explore, but each of those paths may have greater potential to lead somewhere interesting.

While the first image of black hole shadows offers an incredible view of our universe, it also provides physical evidence that Einstein was right. But cosmic confirmation doesn’t mean that his theory is unassailable. Rather, increased scrutiny of the theory could offer new windows of scientific opportunity.