How Fast Are You Moving Right Now

Understanding Speed: How Fast Are You Moving?

How fast are you moving right now? This may seem like a straightforward question, but the answer is far from simple. You might initially think, “I’m not moving.” However, upon further reflection, you may consider the Earth’s motion. This could lead to a second answer, “19 miles/second around the Sun.” But then, you might remember that the Sun moves around the center of the Milky Way galaxy, and the Milky Way moves within the Local Group of galaxies, and so on. Thus, the question “How fast are you moving?” is not as easy as it first appears.

Relative Speed and Standard of Rest

When Mission Control informs astronauts of their speed, there’s always an assumed standard of rest. Initially, speeds are given relative to the launchpad. However, as the journey progresses and the launchpad becomes just another arbitrary place on Earth’s spinning surface, speeds are given relative to the idealized, non-spinning pinpoint center of Earth. This highlights the complexity of answering the question, “How fast are you moving?”

Speed: A Relative Quantity

Speed is a relative quantity. For instance, when Captain Kirk asks Lieutenant Sulu if the Starship Enterprise has reached a speed of warp 7, Sulu should reply, “Relative to what, Captain?” This response, while potentially troublesome for Starfleet officers, is the only accurate answer to the question, “How fast are you moving?” This concept is not based on Einsteinian relativity, but on Galilean relativity, which asserts that there is no such thing as an absolute speed. Speeds are relative, meaning they only have meaning when referred to a reference frame.

Speed, Rest, and Relativity

Even the concept of rest is relative. Earth’s speed is 19 miles/second relative to the Sun. The Enterprise’s speed is warp 7 relative to the center of the Milky Way galaxy. Your speed is zero relative to your easy chair. However, depending on where you sit, it could be hundreds of miles/hour relative to Earth’s center. When we ask, “But how fast is Earth really moving?” we imagine Spaceship Earth plowing through the ocean of space as it orbits the Sun. But space is not an ocean. It has no substance like water. Space is not a thing; space is nothing. You can move between two points in space, but you can’t move through space. There’s nothing to move through.

Relative and Absolute Motion

Some motions have only relative meaning, but some motions have absolute meaning, are absolutely real. For example, constant speed is relative, but change in speed is absolute. When your spaceship fires its engines, your change in speed is beyond doubt. You feel it in your stomach, and your ship’s sensors can measure it. The same goes for rotation. If your spaceship is spinning, you can feel it, and your ship’s sensors can measure it. So, some motions are relative, and some are not. There is no deep reality about constant speed, but changes in speed are deeply real, and so are rotations.

Identifying What is Deeply Real

We have to be thoughtful in our analysis of everyday experience in order to identify what is deeply real. Since we can be fooled by perceptions as basic as speed, maybe every perception deserves careful scrutiny. This is what inspired Einstein to his incredible insights about the speed of light and forward time travel. Knowing how to identify what is deeply real is tough and important work. If a police officer ever pulls you over for speeding and asks, “Do you know how fast you were going?” an insightful, though perhaps unwise, reply would be, “Relative to what?” And then, as you sit in the backseat of the police car and feel it accelerate toward jail, you can add, “But some things are absolute!”