The Astrophysics Spectator

Home

Topics

Interactive Pages

Commentary

Other Pages

Information

Commentary

Perception

Does our knowledge change how we perceive the world around us? In the morning, I see the sun rise. I see the Sun in motion across the sky because I have no sense of Earth's motion. My intellect cannot counteract my senses. My knowledge of astronomy does not change how I perceive my surroundings.

We live our lives in a three-dimensional world that only approximates the universe. We perceive a wall as an infinitely divisible surface despite knowing it is a collection of atoms. We perceive time as moving at the same rate for everyone despite knowing that the passage of time is altered for those who are accelerating. We perceive light as traveling instantaneously despite knowing that light moves at a finite velocity. Despite our knowledge, we cannot escape our perceptions.

When I was writing the pages discussing astronomical distance, I became aware of just how alienated we are in our daily experiences from the universe that we know. Earth's yearly motion around the Sun causes the nearest stars to move back and forth on the sky by less than two arc seconds. Normally I just see this value without feeling how very small it is. Saying that an arc second is one-sixtieth of an arc minute is too abstract to have much impact. But when I realized that two arc seconds. is about the angular diameter of one of Jupiter's moons on the sky, and knowing that Jupiter itself appears to my eyes as a point, I began to comprehend just how small this size is. I am amazed that astronomers can measure such a tiny value.

Years ago, a standard film shown to students of physics was Powers of Ten. I see that someone has placed a modern version on the web. In this film, the camera pulls away from a couple picnicking on a lawn, with the scale of the frame increasing by a factor of ten every ten seconds. You see the couple rapidly shrink to a point as the shot becomes first an aerial view, and then a view from space. Rapidly the frame pulls in the whole Earth, the Moon, and then the planets, which shrink with the Sun to insignificance. And then nothing. Time goes on, but the background stars remain fixed as the frame takes in geometrically increasing volumes of space, until finally the stars begin to come together to reveal the Galaxy. In this way, the film helps bring to a human level an abstraction that is beyond human experience.

In astrophysics, we often encounter factors of ten raised to very high powers—not 1010, but more like 1050. How does one develop a sense for these immense scales? In general one cannot. My normal thoughts when encountering these large factors is not “wow, that's big,” but “how am I going to multiply these numbers without overflowing my calculator.” We push the scales out of our minds, and instead we concentrate on the physical process and the equations that describe them. Our focus is not on the immense mathematical factors, but on a handful of equations, with the offending factors masked as single-letter constants and variables. The immense scales are forgotten, and we lose a sense of scale.

The universe as we understand it is outside of human experience, and we encapsulate it in mathematics that hides the scale of the universe. Because of these things, our understanding of the universe is divorced from our sense of the world.

Jim Brainerd

Ad image for The Astrophysics Spectator.