The following post is by Jeffrey Bennett, author of What Is Relativity?: An Intuitive Introduction to Einstein’s Ideas, and Why They Matter
Black holes don’t suck. It’s a point I’ve emphasized to students for decades, and I even considered it as a possible title for my book at one point. So why, then, do so many people assume that a spaceship passing near a black hole would get “sucked in,” or that transforming the Sun into a black hole would cause Earth and the other planets to be sucked in?
It’s an interesting question, because the answer tells us something about our system of science education. Society and public knowledge have changed dramatically in many ways since Einstein published his general theory of relativity in 1915. Consider, for example, that in 1915: Flight was only a few years old, automobiles were still rare, antibiotics were decades from discovery, life expectancy was decades shorter than today, and women still did not have the right to vote in U.S. national elections. But at least one thing has not changed: Most people today still assume space and time to be just as fixed and independent as did our ancestors, even though we are approaching the 100th anniversary of Einstein’s theory that showed otherwise.
It may seem that no one is harmed by this lack of public understanding, but I’d argue otherwise. For example, I believe that all human beings live their lives according to a world view with which they see their place in the world and universe, and this in turn makes it seem important to have a world view that is consistent with reality. And reality, as it turns out, is the real topic of Einstein’s theory of relativity, because it is the theory that describes our current understanding of space, time, and gravity. As such, it provides the foundation of almost all of modern physics and astronomy, which means it tells us how the universe — our reality — actually works. I’d be exaggerating only slightly if I said that knowing something about relativity is as important to having a true “cosmic perspective” as recognizing that Earth is a planet going around the Sun rather than the center of the universe.
Relativity is also a great way to introduce students (and the public) to the way in which science works, and to the real meaning of a scientific theory. In fact, relativity is arguably our best example of how one theory (in this case Newton’s theory of gravity) can be replaced by another (Einstein’s general theory of relativity) without the first one being “wrong.” In this case, relativity expanded the range of situations in which we can calculate gravitational effects, but still gives essentially the same answers as Newton’s earlier theory of gravity for most situations. In my opinion, there’s no better way to explain the nature of scientific evidence and the means by which we test hypotheses until the evidence becomes strong enough to consider them theories. I suspect that if we taught this example in schools, we’d be able to build upon it to quiet much of the public debate that arises over other scientific topics, including evolution and climate change.
Of course, the way in which Einstein built upon Newton’s work also brings us back to the question about black holes. They don’t suck because, as long as you are not very close to a black hole, Newton’s law of gravity gives the same answers as relativity, and Newton’s law allows only for orbits, not for being “sucked in.” As to why so many people nevertheless harbor visions of black holes as cosmic vacuum cleaners, the answer is the lack of relativity in education: When we leave major gaps in education, such as failing to teach kids about something as exciting and amazing as black holes, it’s unsurprising that ignorance rushes in to fill the gaps.
So my take-away point for the day is this: Relativity is important, and that means it should be taught. The level will vary with students and interests, but everyone should learn something about it. As an analogy, for most people, it suffices to know that Earth orbits the Sun, without knowing the detailed parameters of Earth’s orbit, or the specific ways in which those parameters are affected by the influences of other planets. In the same way, everyone should know something about the basic nature of space, time, and gravity, even if only a few will ever learn the details and mathematics of it.